The present invention relates to a synchronization arrangement for a planetary gear.
In transmission systems for heavy-duty vehicles, for example trucks, it is known to connect a supplementary gearbox to the main gearbox of the vehicle for the purpose of doubling the number of gear change possibilities. Such a supplementary gearbox usually comprises a planetary gear, by means of which the gear change possibilities of the drive unit can be divided into a low gear range and a high gear range. In the low gear range use is made of gear changing in the planetary gear, while in the high gear range no gear changing takes place in the planetary gear.
It is also known to design such planetary gears with synchronization arrangements for the purpose of facilitating gear changing during running. The positioning of the synchronization arrangements and the coupling members necessary for the gear change maneuvering may vary.
In one embodiment, which is advantageous from the point of view of power distribution, the ring wheel of the planetary gear constitutes a coupling muff which, by means of axial displacement, can be brought into engagement with coupling rings on either axial side of the planetary gear. An embodiment of this type is described in greater detail in Swedish Patent Specification SE 453,379 (and corresponding specifications U.S. Pat. No. 4,821,591 and EP 0,239,555).
In this embodiment, a number of tangentially directed springs effect a rotation, limited relative to the ring wheel, of the synchronization rings in such a way that locking teeth arranged on these assume, during a synchronization phase, a position which locks the gear movement.
In contrast, when synchronous rotation has been achieved, it is possible, under the counteraction of the springs, to turn the synchronization rings and move the ring wheel/coupling sleeve axially for coupling together with a coupling ring.
One disadvantage of this embodiment is that the springs act only in one direction, and as a result of this a predetermined direction of rotation is assumed. When the planetary gear is used as illustrated as a supplementary gearbox, this means that synchronization is only possible when driving forwards and, therefore, not when reversing. The possibilities of using a planetary gear of this type in other applications are limited, for example in a gearbox consisting of several planetary gears with alternating directions of rotation. This known planetary gear is also disadvantageous from the manufacturing and assembly point of view, which also means that it is a relatively expensive solution.
Patent application Ser. No. 7807692-4 describes another embodiment in which each of the synchronization rings is connected to a plate collar designed with axial, resilient tongues. These tongues engage in internal circumferential grooves in the ring wheel and are intended, on the one hand, to connect the ring wheel to the respective synchronization ring with a locking effect and, on the other hand, to dampen relative vibratory movements between the ring wheel and the synchronization rings. The formation of grooves in the ring wheel encroaches on its cog tracks, which must therefore be made correspondingly larger in the axial direction, and this means that the dimensions of the whole transmission increase in the axial direction.
Patent Specification DE 1,750,546 describes another embodiment in which the synchronization rings are designed with a number of radial shoulders engaging recesses formed for this purpose on the inside of the ring wheel. By means of designing the recesses with a longer extent than the shoulders in the peripheral direction, the synchronization rings are afforded a certain possibility of rotation relative to the ring wheel. However, no further details are given on how this relative rotation possibility takes place. The formation of the internal recesses in the ring wheel limits the ring wheel cogs to a corresponding extent. In order to ensure engagement between ring wheel and planet wheels under all circumstances, the recesses must be positioned at a sufficient distance axially from the planet wheels. This results in the ring wheel having a long axial extent.
In both the abovementioned embodiments the ring wheel can be connected to the output shaft in order to obtain direct gear. This is disadvantageous from the point of view of power distribution since the gear is then subjected internally to high forces.